Not Applicable
Not Applicable
The present invention relates to fiber optic gyroscopes (hereinafter referred to as xe2x80x9cFOGxe2x80x9d), and more particularly, to FOG coils constructed and arranged to withstand severe environmental conditions such as those found in aerospace applications.
A FOG is used to measure the rate of rotation of a vehicle or other platform to which the FOG is attached. The FOG typically includes a coil of optical fiber disposed about an axis of rotation. A light source transmits light into each end of the optical fiber, so that two light transmissions propagate through the optical fiber in counter rotating directions. Detection circuitry receives the light transmissions as they emerge from the ends of the optical fiber and measures the relative phase relationship of the light. The phase relationship of the two light transmissions is related to the angular rotation of the FOG coil about the axis of rotation, and may be used to derive an output that is indicative of the rate of rotation of the FOG coil.
Often it is desirable to use a FOG in applications that encounter significant stresses due to acceleration, vibration, shock, extreme temperature variations, etc. Examples of such applications include aerospace platforms and space launch vehicles, among others. One disadvantage to prior art FOG configurations is that they typically exhibit adverse effects when subjected to forces near 50 g or greater, primarily due to force-induced deformations of the optical coil that affect the coil""s propagation characteristics. In particular, tests have shown that the xe2x80x9cpigtailxe2x80x9d portion of a FOG is the component most susceptible to environmental stresses. To meet performance criteria of design specifications related to aerospace applications, a FOG would preferably be capable of withstanding forces well beyond 50 g.
It is an object of the present invention to substantially overcome the above-identified disadvantages and drawbacks of the prior art.
The following U.S. Patents provide additional background information related to the present invention.
U.S. Pat. No. 6,137,940, Reel of optical fiber, assigned to Alcatel corporation of Paris France, describes a reel of optical fiber comprising a supporting former and a coil made up of a plurality of superposed layers of touching turns of an optical fiber, a link layer made of a flexible material being disposed directly on the supporting former between said former and said coil, wherein an intermediate support made up of a winding of a plurality of layers of the same optical fiber as that of said coil, and wound in the same way, but with the turns glued together with a glue having strong adhesive power, is further situated between said coil and said flexible link layer.
U.S. Pat. No. 6,038,025, Method for manufacturing of fiber optic gyroscopes by providing a flexible connector connected to the coil and remaining gyroscope elements, assigned to Honeywell Inc. (Minneapolis, Minn.) describes a method for fabricating a fiber optic gyroscope and the fiber optic gyroscope produced thereby are disclosed. The method and apparatus are characterized in that optical coils are connected to a substantially rigid member through flexible connectors, thereby enabling a modular unit with increased mobility and accessibility. Multiple assemblies may be arranged to enable the formation of multi-axis fiber optic rotation rate sensors
U.S. Pat. No. 5,973,783, An improved dressing for the fiber optic leads of a fiber optic gyroscope sensing coil and method for forming the same, assigned to Litton Systems, Inc. (Woodland Hills, Calif.) describes a pair of fiber optic leads connecting the sensing coil of a rotation sensing device to an integrated optics chip. The fiber optic leads are originally arranged to extend around the fiber optic sensing coil in different directions. The leads are formed of unequal lengths, where the longer of the leads is extended along an outer circumference of the sensing coil. The longer lead is bent so that the circumferential direction of longer lead reverses itself, and the longer lead then extends around the sensing coil in the same direction as the shorter lead. A low modulus adhesive is applied to the leads and cured to initially bond the leads in place against the sensing coil. The pair of leads is then wound in the same circumferential direction adjacent to each other fashion around the outer circumference of the sensing coil. After the desired amount of winding has been completed, a predetermined length of each of the leads is left available to be routed to the rotation sensing device. The entire outer surface of the wound fiber optic leads surrounding the temporary adhesion is then coated with a low modulus adhesive and cured to bond the wound leads against the sensing coil structure.
U.S. Pat. No. 5,923,807, Storage Apparatus for Optical Fiber, assigned to Lucent Technologies Inc. (Murray Hill, N.J.) describes an optical fiber buffer loop management system which may be incorporated into a conventional interconnection box and which comprises one or more spools or pins around which optical fiber buffer loops are loosely dressed. Strategically placed cover guards forming narrow insertion slots for the fibers are attached to the tops of the spools or pins to prevent the fibers from unraveling. By loosely dressing the fiber loops in the interconnection box, no excess slack exists in the portion of the loop running from the spool to the point at which the plug connector on the end of the buffer loop is connected to the coupling located inside of the interconnection box. Preferably, each of the buffer loops is loosely wrapped about two spools in a figure-of-eight configuration, which allows a buffer loop density approximately four times greater than that of the prior art systems to be achieved without bending the fibers beyond their minimum bend radii. By loosely retaining the buffer loops in the interconnection box, as opposed to wrapping them tautly, the buffer loops can be easily unraveled when repairs are to be made. The present invention also provides a method for replacing faulty plug connectors. In order to replace a faulty plug connector, the plug connector is removed from the coupling device in the interconnection box and the optical fiber is cut so as to separate the plug connector from the optical fiber. The optical fiber is then removed from around the spool or spools and a new plug connector is then secured to the optical fiber. The new plug connector is then connected to the coupling device. The buffer loop is then wrapped about the spools in a figure-of-eight configuration as discussed above.
U.S. Pat. No. 5,481,358, Coil mounting arrangement for fiber optic gyroscope using a gel loaded with particles, assigned to Andrews Corporation (Orland Park, Ill.), describes the sensing coil of a fiber optic gyroscope is wholly or partially surrounded by a gel. The components attached to the coil, such as the directional coupler(s) and polarizer, may also be wholly or partially submerged in the gel. The gel is contained by a rigid housing, in which the inner walls of the housing form a cavity for the coil and the gel. The cavity is filled with the gel, and the gel may be bonded to the inner walls of the housing. The gel remains stiff enough to maintain the coil in a fixed position relative to the housing, and soft enough to avoid any significant effect on the h of the coil over the operating temperature range. Furthermore, the gel can be loaded with particles to adjust the specific gravity of the gel, to modify the thermal properties of the gel and to increase the viscosity of the gel for improved vibration damping. In a modified form, the optical-fiber sensing coil is positioned on a mounting surface and otherwise surrounded by the gel. Alternatively, the optical fiber sensing coil is wound around a form that has a layer of gel on the coil-supporting surface.
U.S. Pat. No. 5,220,632, A method for preparing an optical fiber canister, assigned to Hughes Aircraft Company, Los Angeles, Calif. includes providing a length of a wire having a diameter of about that of the optical fiber, and winding the wire onto a mandrel in a preselected winding pattern to form a base layer. A replicating strip having a flexible substrate with a patterning layer of b-staged epoxy on one side thereof is provided, and the patterning layer is pressed against the base layer to form a groove pattern in the patterning layer. The b-staged epoxy layer is cured to harden it to preserve the groove pattern, and then the flexible substrate is applied to an optical fiber bobbin with the grooved patterning layer facing outwardly. An optical fiber is wound into the groove of the patterning layer to form an optical fiber pack.
One aspect of the invention comprises an optical fiber coil assembly for use in a fiber optic gyroscope, including a bobbin disposed about a longitudinal axis. The longitudinal axis is an axis of rotation about which the bobbin revolves. The coil assembly also includes an optical fiber having a first end and a second end, and further characterized by an intermediate point between the first end and the second end. A first section of the optical coil defined from the intermediate point to the first end is wound around the bobbin in a first rotational direction about the axis of rotation. A second section of the optical coil is defined from the intermediate point to the second end, and at least a portion of the second section is wound around the bobbin in a second rotational direction opposite of the first rotational direction. The coil assembly also includes a reversal of the optical fiber in the second section, such that an end portion of the second section, from the reversal to the second end, is wound around the bobbin in the first direction, along with an end portion of the first section. The coil assembly further includes an epoxy zipper disposed between at least a portion of the first section and the second section of the optical fiber, so as to join the first section and the second section of the optical fiber to form a fiber lead pair. The coil assembly also includes an epoxy bridge disposed between at least a portion of the fiber lead pair and the bobbin, so as to secure the fiber lead pair to the bobbin.
Another embodiment of the invention further includes an integrated optics circuit rotatably mounted to an end of the bobbin, such that the integrated optics circuit rotates about the axis of rotation. The first end and the second end of the optical fiber is fixedly attached and optically coupled to the integrated optics circuit.
Another embodiment of the invention further includes one or more layers of wound fiber, each of the layers being substantially parallel to the axis of rotation, and an epoxy layer disposed upon the outer portion of each of the one or more layer of wound fiber.
In another embodiment of the invention, a group of individual optical fibers are constructed and arranged such that a cross section of the one or more layers of wound fiber are disposed in a hexagonal arrangement.
Another embodiment of the invention further includes an epoxy layer disposed between a first layer of the one or more layers of wound fiber and the bobbin.
In another embodiment of the invention, the epoxy layer includes a high-modulus epoxy.
In another embodiment of the invention, the epoxy zipper extends along the fiber lead pair from the ends of the fiber to the reversal.
In another embodiment of the invention, the reversal is positioned within the fiber such that the end portion of the first section is substantially equal to the end portion of the second section.
In another embodiment of the invention, the epoxy zipper is disposed along opposite sides of the first section and the second section of the optical fiber, such that the first section and the second section of the optical fiber are substantially adjacent.
In another embodiment of the invention, the epoxy zipper is disposed between the first section and the second section of the optical fiber, such that the zipper maintains the first section and the second section of the optical fiber at a fixed distance from one another along the length of the fiber lead pair.
In another embodiment of the invention, the epoxy zipper encapsulates the first section and the second section of the optical fiber and fixedly maintains the first section and the second section with respect to one another along the length of the fiber lead pair.
In another aspect, the invention comprises an optical fiber coil assembly for use in a fiber optic gyroscope, including a bobbin disposed about a longitudinal axis. The longitudinal axis is an axis of rotation about which the bobbin revolvees. The coil assembly also includes an optical fiber having a first end and a second end. The fiber is characterized by an intermediate point between the first end and the second end. A first section of the optical coil defined from the intermediate point to the first end is wound around the bobbin in a first rotational direction about the axis of rotation. A second section of the optical coil defined from the intermediate point to the second end is wound, at least partially, around the bobbin in a second rotational direction opposite of the first rotational direction. The coil assembly further includes an epoxy zipper disposed between at least a portion of the first section and the second section of the optical fiber, so as to join the first section and the second section of the optical fiber to form a fiber lead pair. The coil assembly also includes an epoxy bridge disposed between at least a portion of the fiber lead pair and the bobbin, so as to secure the fiber lead pair to the bobbin.
In another aspect, the invention comprises an optical fiber coil assembly for use in a fiber optic gyroscope, including a bobbin, disposed about a longitudinal axis. The longitudinal axis is an axis of rotation about which the bobbin revolves. The coil assembly further includes an optical fiber having a first end and a second end. The fiber is characterized by an intermediate point between the first end and the second end. A first section of the optical coil defined from the intermediate point to the first end is wound around the bobbin in a first rotational direction about the axis of rotation. A second section of the optical coil defined from the intermediate point to the second end is at least partially wound around the bobbin in a second rotational direction opposite of the first rotational direction. The coil assembly further includes an integrated optics circuit rotatably mounted to an end of the bobbin, such that the integrated optics circuit rotates about the axis of rotation. The first end and the second end of the optical fiber is fixedly attached and optically coupled to the integrated optics circuit.
In another aspect, the invention comprises an optical fiber coil assembly for use in a fiber optic gyroscope, including a bobbin disposed about a longitudinal axis. The longitudinal axis is an axis of rotation about which the bobbin revolves. The coil assembly further includes an optical fiber having a first end and a second end. The optical fiber is characterized by an intermediate point between the first end and the second end. A first section of the optical coil defined from the intermediate point to the first end is wound around the bobbin in a first rotational direction about the axis of rotation. A second section of the optical coil defined from the intermediate point to the second end is wound, at least partially, around the bobbin in a second rotational direction opposite of the first rotational direction. The coil assembly further includes an epoxy zipper disposed between at least a portion of the first section and the second section of the optical fiber, so as to join the first section and the second section of the optical fiber to form a fiber lead pair.
In another aspect, the invention comprises an optical fiber coil assembly for use in a fiber optic gyroscope, including a bobbin disposed about a longitudinal axis. The longitudinal axis is an axis of rotation about which the bobbin revolves and the coil assembly further includes an optical fiber having a first end and a second end. The optical fiber is characterized by an intermediate point between the first end and the second end. A first section of the optical coil defined from the intermediate point to the first end is wound around the bobbin in a first rotational direction about the axis of rotation. A second section of the optical coil defined from the intermediate point to the second end is wound, at least partially, around the bobbin in a second rotational direction opposite of the first rotational direction. The coil assembly further includes a reversal of the optical fiber in the second section, such that an end portion of the second section, from the reversal to the second end, is wound around the bobbin in the first direction, along with an end portion of the first section. The coil assembly also includes an epoxy zipper disposed between at least a portion of the first section and the second section of the optical fiber, so as to join the first section and the second section of the optical fiber to form a fiber lead pair. The coil assembly also includes an epoxy bridge disposed between at least a portion of the fiber lead pair and the bobbin, so as to secure the fiber lead pair to the bobbin. The coil assembly further includes an integrated optics circuit rotatably mounted to an end of the bobbin, so that the optics circuit rotates about the axis of rotation. The first end and the second end of the optical fiber is fixedly attached and optically coupled to the integrated optics circuit. The optical fiber is constructed and arranged as one or more layers of wound fiber, each of the layers being substantially parallel to the axis of rotation, and an epoxy layer is disposed upon the outer portion of each of the one or more layer of wound fiber.
In another aspect, the invention comprises a method of constructing an optical fiber coil assembly for use in a fiber optic gyroscope. The method includes winding an optical fiber about a bobbin, beginning at an intermediate point on the fiber between a first end and a second end. A first section of the optical fiber is defined from the intermediate point to the first end. This first section of the coil is wound around the bobbin in a first rotational direction about the axis of rotation. A second section of the optical coil defined from the intermediate point to the second end. This second section is wound, at least partially, around the bobbin in a second rotational direction opposite of the first rotational direction. The optical fiber is constructed and arranged as one or more layers of wound fiber, and each of the layers is substantially parallel to the axis of rotation. An epoxy layer is disposed upon the outer portion of each of the one or more layer of wound fiber. The method also includes providing a reversal of the optical fiber in the second section, such that an end portion of the second section, from the reversal to the second end, is wound around the bobbin in the first direction, along with an end portion of the first section. The method further includes applying an epoxy zipper disposed between at least a portion of the first section and the second section of the optical fiber, so as to join the first section and the second section of the optical fiber to form a fiber lead pair. The method also includes applying an epoxy bridge disposed between at least a portion of the fiber lead pair and the bobbin, so as to secure the fiber lead pair to the bobbin. The method further includes rotatably mounting an integrated optics circuit to an end of the bobbin, such that the integrated optics circuit rotates about the axis of rotation. The first end and the second end of the optical fiber is fixedly attached and optically coupled to the integrated optics circuit.
In another aspect, the invention comprises a method of constructing an optical fiber coil assembly for use in a fiber optic gyroscope. The method includes winding an optical fiber about a bobbin, beginning at an intermediate point on the fiber between a first end and a second end. A first section of the optical fiber is defined from the intermediate point to the first end. This first section of the coil is wound around the bobbin in a first rotational direction about the axis of rotation. A second section of the optical coil defined from the intermediate point to the second end. This second section is wound, at least partially, around the bobbin in a second rotational direction opposite of the first rotational direction. The optical fiber is constructed and arranged as one or more layers of wound fiber, and each of the layers is substantially parallel to the axis of rotation. An epoxy layer is disposed upon the outer portion of each of the one or more layer of wound fiber. The method also includes applying an epoxy zipper disposed between at least a portion of the first section and the second section of the optical fiber, so as to join the first section and the second section of the optical fiber to form a fiber lead pair.
In another embodiment, the method further includes applying an epoxy bridge disposed between at least a portion of the fiber lead pair and the bobbin, so as to secure the fiber lead pair to the bobbin.
In another embodiment, the method further includes rotatably mounting an integrated optics circuit to an end of the bobbin, such that the integrated optics circuit rotates about the axis of rotation. The first end and the second end of the optical fiber is fixedly attached and optically coupled to the integrated optics circuit.
In another embodiment, the method further includes providing a reversal of the optical fiber in the second section, such that an end portion of the second section, from the reversal to the second end, is wound around the bobbin in the first direction, along with an end portion of the first section.
In another aspect, the invention comprises an optical fiber coil assembly for use in a fiber optic gyroscope. The coil assembly includes an optical fiber having a first end and a second end, and is characterized by an intermediate point between the first end and the second end. A first section of the optical coil is defined from the intermediate point to the first end, and a second section is defined from the intermediate point to the first end. The first section is wound around a bobbin in a first rotational direction about the axis of rotation, and the second section is wound around the bobbin in a second rotational direction opposite of the first rotational direction. The coil assembly further includes means for reversing the optical fiber in the second section, such that an end portion of the second section, from the reversal to the second end, is wound around the bobbin in the first direction, along with an end portion of the first section. The coil assembly also includes means for joining the first section and the second section of the optical fiber to form a fiber lead pair, and means for bridging at least a portion of the fiber lead pair with respect to the bobbin, so as to secure the fiber lead pair to the bobbin.